div {
  background-color: red;
  width: 100px;
  height: 200px;
  border-style: solid;
  border-width: 1px;
  border-color: black;
}
div .in {
  background-color: blue;
  width: 50px;
  height: 50px;
}
div:hover {
  background-color: green;
}